I played with some bore scopes a few years ago. Nothing "cheap" was worth it. Today I shoved the Teslong down my Tikka 6.5x55. First rifle I scoped with it. Wow. Clarity is nice. I think to get a feel of what one is looking at will require practice, but its definitely possible. I could see the throat mill marks clearly, some erosion, and various patches of "something" in the bore the whole length. This gun has not been cleaned in too long (shoots well, has hunting loads plenty loaded in advance).
Anyhow, I saw better pics of a bore than I've ever seen with my own personal camera before, ever. For $50, a deal.
I think for it to be useful, we will need to scope more guns, more often and see what cleaning, shooting, etc do over time. My first take is: as advertised, 6.5x55 swede is easy on the bore. Has around 500 down the tube and I still see mill marks in the throat...... And the Teslong is worth the $
I plan to basically hang it up and never coil it again, based on the experiences noted here and on reviews on Amazon etc.....